What is Oncology? What is Oncology? By Dr Ananya Mandal, MD The term oncology literally means a branch of science that deals with tumours and cancers. The word “onco” means bulk, mass, or tumor while “-logy” means study. What is cancer? Each of the cells of the body have a tightly regulated system that controls their growth, maturity, reproduction and eventual death. Cancer begins when cells in a part of the body start to grow out of control. There are many kinds of cancer, but they all start because of out-of-control growth of abnormal cells. How common is cancer? Today, millions of people are living with cancer or have had cancer. Cancer is the second leading cause of death in the United States. About one-half of all men and one-third of all women in the US will develop cancer during their lifetimes. How long has cancer existed for? Some of the earliest evidence of cancer is found among fossilized bone tumors, human mummies in ancient Egypt, and ancient manuscripts. Abnormalities suggestive of the bone cancer called osteosarcoma have been seen in mummies.

Among manuscripts the first known description of cancer is seen in the Edwin Smith Papyrus and is a copy of part of an ancient Egyptian textbook on trauma surgery. It describes 8 cases of tumors or ulcers of the breast that were treated by cauterization with a tool called the fire drill. It dates back to about 3000 BC. The papyrus describes the condition as “incurable”. Role of an oncologist Medical professionals who practice oncology are called Cancer specialists or oncologists. These oncologists have several specific roles. They help in diagnosis of the cancer, help in staging the cancer and grading the aggressive nature of the cancer. Oncology diagnostic tools The most important diagnostic tool remains the clinical history of the patient. Common symptoms that point towards cancer include fatigue, weight loss, unexplained anemia, fever of unknown origin etc. Oncology depends on diagnostic tools like biopsy or removal of bits of the tumour tissue and examining it under the microscope. Other diagnostic tools include endoscopy for the gastrointestinal tract, imaging studies like X-rays, CT scanning, MRI scanning, ultrasound and other radiological techniques, Scintigraphy, Single Photon Emission Computed Tomography, Positron emission tomography and nuclear medicine techniques etc.

Related Stories Cancer Center: Types, Symptoms, Causes, Tests, and Treatments, Including Chemo and Radiation Do you know all your options? Cancer Overview Cancer, also called malignancy, is an abnormal growth of cells. There are more than 100 types of cancer, including breast cancer, skin cancer, lung cancer, colon cancer, prostate cancer, and lymphoma. Symptoms vary depending on the type. Cancer treatment may include chemotherapy, radiation, and/or surgery. latest headlines Cancer: Facts, Causes, Symptoms and Research knowledge center home » cancer » facts, causes and research Cancer: Facts, Causes, Symptoms and Research What is Cancer? Treatments and Prevention Cancer is a class of diseases characterized by out-of-control cell growth. There are over 100 different types of cancer, and each is classified by the type of cell that is initially affected. Cancer harms the body when altered cells divide uncontrollably to form lumps or masses of tissue called tumors (except in the case of leukemia where cancer prohibits normal blood function by abnormal cell division in the blood stream). Tumors can grow and interfere with the digestive, nervous, and circulatory systems, and they can release hormones that alter body function.

Tumors that stay in one spot and demonstrate limited growth are generally considered to be benign. More dangerous, or malignant, tumors form when two things occur: a cancerous cell manages to move throughout the body using the blood or lymphatic systems, destroying healthy tissue in a process called invasion that cell manages to divide and grow, making new blood vessels to feed itself in a process called angiogenesis. When a tumor successfully spreads to other parts of the body and grows, invading and destroying other healthy tissues, it is said to have metastasized. This process itself is called metastasis, and the result is a serious condition that is very difficult to treat. According to the American Cancer Society, Cancer is the second most common cause of death in the US and accounts for nearly 1 of every 4 deaths. The World Health Organisation estimates that, worldwide, there were 14 million new cancer cases and 8.2 million cancer-related deaths in 2012 (their most recent data). Individual types of cancer There are said to be over 200 different types of cancer. We have the following common cancer types covered in individual Knowledge Center articles: Vulvar cancer Latest cancer research We are a leading publisher of worldwide cancer news and research.

You can find all our latest news in our cancer news section . The rest of this article will focus on what cancer is, what causes cancer, the symptoms, diagnosis and available treatments. Fast facts on cancer Here are some key points about cancer. More detail and supporting information is in the main article. More than 575,000 people die of cancer, and more than 1.5 million people are diagnosed with cancer per year in the US. Cancer is considered to be one of the leading causes of morbidity and mortality worldwide. The financial costs of cancer in the US per year are an estimated $263.8 billion in medical costs and lost productivity. African Americans are more likely to die of cancer than people of any other race or ethnicity. It is believed that cancer risk can be reduced by avoiding tobacco, limiting alcohol intake, limiting UV ray exposure from the sun and tanning beds and maintaining a healthy diet, level of fitness and seeking regular medical care. Screening can locate cervical cancer, colorectal cancer and breast cancer at an early, treatable stage. Vaccines such as the human papillomavirus (HPV) vaccine assists in preventing some cervical, vaginal, vulvar, and oral cancers.

A vaccine for hepatitis B can reduce liver cancer risk. According to the World Health Organization (WHO), the numbers of new cancer cases is expected to rise by about 70% over the next 20 years. The most common sites of cancer among men are lung, prostate, colon, rectum, stomach and liver. The most common sites of cancer among women are breast, colon, rectum, lung, cervix and stomach. How cancer spreads Scientists reported in Nature Communications (October 2012 issue) that they have discovered an important clue as to why cancer cells spread . It has something to do with their adhesion (stickiness) properties. Certain molecular interactions between cells and the scaffolding that holds them in place (extracellular matrix) cause them to become unstuck at the original tumor site, they become dislodged, move on and then reattach themselves at a new site. The researchers say this discovery is important because cancer mortality is mainly due to metastatic tumors, those that grow from cells that have traveled from their original site to another part of the body. These are called secondary tumors. Only 10% of cancer deaths are caused by the primary tumors.

The scientists, from the Massachusetts Institute of Technology, say that finding a way to stop cancer cells from sticking to new sites could interfere with metastatic disease, and halt the growth of secondary tumors. Malignant cells are more agile than non-malignant ones Scientists from the Physical Sciences-Oncology Centers, USA, reported in the journal Scientific Reports (April 2013 issue) that malignant cells are much “nimbler” than non-malignant ones . Malignant cells can pass more easily through smaller gaps, as well as applying a much greater force on their environment compared to other cells. Professor Robert Austin and team created a new catalogue of the physical and chemical features of cancerous cells with over 100 scientists from 20 different centers across the United States. The authors believe their catalogue will help oncologists detect cancerous cells in patients early on, thus preventing the spread of the disease to other parts of the body. Prof. Austin said "By bringing together different types of experimental expertise to systematically compare metastatic and non-metastatic cells, we have advanced our knowledge of how metastasis occurs." Causes of cancer Cancer is ultimately the result of cells that uncontrollably grow and do not die.

Normal cells in the body follow an orderly path of growth, division, and death. Programmed cell death is called apoptosis, and when this process breaks down, cancer begins to form. Unlike regular cells, cancer cells do not experience programmatic death and instead continue to grow and divide. This leads to a mass of abnormal cells that grows out of control. What is cancer? - Video A short, 3D, animated introduction to cancer. This was originally created by BioDigital Systems and used in the Stand Up 2 Cancer telethon. Genes - the DNA type Cells can experience uncontrolled growth if there are mutations to DNA, and therefore, alterations to the genes involved in cell division. Four key types of gene are responsible for the cell division process: oncogenes tell cells when to divide, tumor suppressor genes tell cells when not to divide, suicide genes control apoptosis and tell the cell to kill itself if something goes wrong, and DNA-repair genes instruct a cell to repair damaged DNA. Cancer occurs when a cell's gene mutations make the cell unable to correct DNA damage and unable to commit suicide. Similarly, cancer is a result of mutations that inhibit oncogene and tumor suppressor gene function, leading to uncontrollable cell growth.

Carcinogens Carcinogens are a class of substances that are directly responsible for damaging DNA, promoting or aiding cancer. Tobacco, asbestos, arsenic, radiation such as gamma and x-rays, the sun, and compounds in car exhaust fumes are all examples of carcinogens. When our bodies are exposed to carcinogens, free radicals are formed that try to steal electrons from other molecules in the body. Theses free radicals damage cells and affect their ability to function normally. Genes - the family type Cancer can be the result of a genetic predisposition that is inherited from family members. It is possible to be born with certain genetic mutations or a fault in a gene that makes one statistically more likely to develop cancer later in life. Cancer and other medical factors As we age, there is an increase in the number of possible cancer-causing mutations in our DNA. This makes age an important risk factor for cancer. Several viruses have also been linked to cancer such as: human papillomavirus (a cause of cervical cancer), hepatitis B and C (causes of liver cancer), and Epstein-Barr virus (a cause of some childhood cancers).

Human immunodeficiency virus (HIV) - and anything else that suppresses or weakens the immune system - inhibits the body's ability to fight infections and increases the chance of developing cancer. On the next page we look at the symptoms of cancer and how cancer is classified and diagnosed. On the final page we discuss treatments for cancer. A site offering an alternate theory on stomach cancer - written by a Japanese physician titled: "Gastric Cancers Analyzed By Theoretical Physics" Recommended related news Disclaimer: This informational section on Medical News Today is regularly reviewed and updated, and provided for general information purposes only. The materials contained within this guide do not constitute medical or pharmaceutical advice, which should be sought from qualified medical and pharmaceutical advisers. Please note that although you may feel free to cite and quote this article, it may not be re-produced in full without the permission of Medical News Today.

For further details, please view our full terms of use © MediLexicon International Ltd Oncology | Definition of Oncology by Merriam-Webster ONCOLOGY Defined for English Language Learners oncology noun on·col·o·gy \än-ˈkä-lə-jē, äŋ-\ Definition of oncology for English Language Learners medical : the study and treatment of cancer and tumors Medical Dictionary What Is Cancer? - National Cancer Institute What Is Cancer? A dividing lung cancer cell. Credit: National Institutes of Health A Collection of Related Diseases Cancer is the name given to a collection of related diseases. In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tissues. Cancer can start almost anywhere in the human body, which is made up of trillions of cells. Normally, human cells grow and divide to form new cells as the body needs them. When cells grow old or become damaged, they die, and new cells take their place. When cancer develops, however, this orderly process breaks down. As cells become more and more abnormal, old or damaged cells survive when they should die, and new cells form when they are not needed.

These extra cells can divide without stopping and may form growths called tumors. Many cancers form solid tumors, which are masses of tissue. Cancers of the blood, such as leukemias, generally do not form solid tumors. Cancerous tumors are malignant, which means they can spread into, or invade, nearby tissues. In addition, as these tumors grow, some cancer cells can break off and travel to distant places in the body through the blood or the lymph system and form new tumors far from the original tumor. Unlike malignant tumors, benign tumors do not spread into, or invade, nearby tissues. Benign tumors can sometimes be quite large, however. When removed, they usually don’t grow back, whereas malignant tumors sometimes do. Unlike most benign tumors elsewhere in the body, benign brain tumors can be life threatening. Differences between Cancer Cells and Normal Cells Cancer cells differ from normal cells in many ways that allow them to grow out of control and become invasive. One important difference is that cancer cells are less specialized than normal cells. That is, whereas normal cells mature into very distinct cell types with specific functions, cancer cells do not. This is one reason that, unlike normal cells, cancer cells continue to divide without stopping.

In addition, cancer cells are able to ignore signals that normally tell cells to stop dividing or that begin a process known as programmed cell death, or apoptosis, which the body uses to get rid of unneeded cells. Cancer cells may be able to influence the normal cells, molecules, and blood vessels that surround and feed a tumor—an area known as the microenvironment. For instance, cancer cells can induce nearby normal cells to form blood vessels that supply tumors with oxygen and nutrients, which they need to grow. These blood vessels also remove waste products from tumors. Cancer cells are also often able to evade the immune system, a network of organs, tissues, and specialized cells that protects the body from infections and other conditions. Although the immune system normally removes damaged or abnormal cells from the body, some cancer cells are able to “hide” from the immune system. Tumors can also use the immune system to stay alive and grow. For example, with the help of certain immune system cells that normally prevent a runaway immune response , cancer cells can actually keep the immune system from killing cancer cells. How Cancer Arises Cancer is a genetic disease—that is, it is caused by changes to genes that control the way our cells function, especially how they grow and divide.

Genetic changes that cause cancer can be inherited from our parents. They can also arise during a person’s lifetime as a result of errors that occur as cells divide or because of damage to DNA caused by certain environmental exposures. Cancer-causing environmental exposures include substances, such as the chemicals in tobacco smoke, and radiation, such as ultraviolet rays from the sun. (Our Cancer Causes and Risk Factors page has more information.) Each person’s cancer has a unique combination of genetic changes. As the cancer continues to grow, additional changes will occur. Even within the same tumor, different cells may have different genetic changes. In general, cancer cells have more genetic changes, such as mutations in DNA, than normal cells. Some of these changes may have nothing to do with the cancer; they may be the result of the cancer, rather than its cause. "Drivers" of Cancer The genetic changes that contribute to cancer tend to affect three main types of genes— proto-oncogenes , tumor suppressor genes , and DNA repair genes. These changes are sometimes called “drivers” of cancer. Proto-oncogenes are involved in normal cell growth and division.

However, when these genes are altered in certain ways or are more active than normal, they may become cancer-causing genes (or oncogenes), allowing cells to grow and survive when they should not. Tumor suppressor genes are also involved in controlling cell growth and division. Cells with certain alterations in tumor suppressor genes may divide in an uncontrolled manner. DNA repair genes are involved in fixing damaged DNA. Cells with mutations in these genes tend to develop additional mutations in other genes. Together, these mutations may cause the cells to become cancerous. As scientists have learned more about the molecular changes that lead to cancer, they have found that certain mutations commonly occur in many types of cancer. Because of this, cancers are sometimes characterized by the types of genetic alterations that are believed to be driving them, not just by where they develop in the body and how the cancer cells look under the microscope. When Cancer Spreads Enlarge In metastasis, cancer cells break away from where they first formed (primary cancer), travel through the blood or lymph system, and form new tumors (metastatic tumors) in other parts of the body. The metastatic tumor is the same type of cancer as the primary tumor.

A cancer that has spread from the place where it first started to another place in the body is called metastatic cancer. The process by which cancer cells spread to other parts of the body is called metastasis. Metastatic cancer has the same name and the same type of cancer cells as the original, or primary, cancer. For example, breast cancer that spreads to and forms a metastatic tumor in the lung is metastatic breast cancer, not lung cancer. Under a microscope, metastatic cancer cells generally look the same as cells of the original cancer. Moreover, metastatic cancer cells and cells of the original cancer usually have some molecular features in common, such as the presence of specific chromosome changes. Treatment may help prolong the lives of some people with metastatic cancer. In general, though, the primary goal of treatments for metastatic cancer is to control the growth of the cancer or to relieve symptoms caused by it. Metastatic tumors can cause severe damage to how the body functions, and most people who die of cancer die of metastatic disease. Tissue Changes that Are Not Cancer Not every change in the body’s tissues is cancer. Some tissue changes may develop into cancer if they are not treated, however.

Here are some examples of tissue changes that are not cancer but, in some cases, are monitored: Hyperplasia occurs when cells within a tissue divide faster than normal and extra cells build up, or proliferate. However, the cells and the way the tissue is organized look normal under a microscope. Hyperplasia can be caused by several factors or conditions, including chronic irritation. Dysplasia is a more serious condition than hyperplasia. In dysplasia, there is also a buildup of extra cells. But the cells look abnormal and there are changes in how the tissue is organized. In general, the more abnormal the cells and tissue look, the greater the chance that cancer will form. Some types of dysplasia may need to be monitored or treated. An example of dysplasia is an abnormal mole (called a dysplastic nevus) that forms on the skin. A dysplastic nevus can turn into melanoma, although most do not. An even more serious condition is carcinoma in situ. Although it is sometimes called cancer, carcinoma in situ is not cancer because the abnormal cells do not spread beyond the original tissue. That is, they do not invade nearby tissue the way that cancer cells do.

But, because some carcinomas in situ may become cancer, they are usually treated. Normal cells may become cancer cells. Before cancer cells form in tissues of the body, the cells go through abnormal changes called hyperplasia and dysplasia. In hyperplasia, there is an increase in the number of cells in an organ or tissue that appear normal under a microscope. In dysplasia, the cells look abnormal under a microscope but are not cancer. Hyperplasia and dysplasia may or may not become cancer. Credit: Terese Winslow Types of Cancer There are more than 100 types of cancer. Types of cancer are usually named for the organs or tissues where the cancers form. For example, lung cancer starts in cells of the lung, and brain cancer starts in cells of the brain. Cancers also may be described by the type of cell that formed them, such as an epithelial cell or a squamous cell. You can search NCI’s website for information on specific types of cancer based on the cancer’s location in the body or by using our A to Z List of Cancers . We also have collections of information on childhood cancers and cancers in adolescents and young adults .

Here are some categories of cancers that begin in specific types of cells: Carcinoma Carcinomas are the most common type of cancer. They are formed by epithelial cells, which are the cells that cover the inside and outside surfaces of the body. There are many types of epithelial cells, which often have a column-like shape when viewed under a microscope. Carcinomas that begin in different epithelial cell types have specific names: Adenocarcinoma is a cancer that forms in epithelial cells that produce fluids or mucus. Tissues with this type of epithelial cell are sometimes called glandular tissues. Most cancers of the breast, colon, and prostate are adenocarcinomas. Basal cell carcinoma is a cancer that begins in the lower or basal (base) layer of the epidermis, which is a person’s outer layer of skin. Squamous cell carcinoma is a cancer that forms in squamous cells, which are epithelial cells that lie just beneath the outer surface of the skin. Squamous cells also line many other organs, including the stomach, intestines, lungs, bladder, and kidneys. Squamous cells look flat, like fish scales, when viewed under a microscope.

Squamous cell carcinomas are sometimes called epidermoid carcinomas. Transitional cell carcinoma is a cancer that forms in a type of epithelial tissue called transitional epithelium, or urothelium. This tissue, which is made up of many layers of epithelial cells that can get bigger and smaller, is found in the linings of the bladder, ureters, and part of the kidneys (renal pelvis), and a few other organs. Some cancers of the bladder, ureters, and kidneys are transitional cell carcinomas. Sarcoma Enlarge Soft tissue sarcoma forms in soft tissues of the body, including muscle, tendons, fat, blood vessels, lymph vessels, nerves, and tissue around joints. Sarcomas are cancers that form in bone and soft tissues, including muscle, fat, blood vessels, lymph vessels , and fibrous tissue (such as tendons and ligaments). Our page on soft tissue sarcoma has more information. Leukemia Cancers that begin in the blood-forming tissue of the bone marrow are called leukemias. These cancers do not form solid tumors.

Instead, large numbers of abnormal white blood cells (leukemia cells and leukemic blast cells) build up in the blood and bone marrow, crowding out normal blood cells. The low level of normal blood cells can make it harder for the body to get oxygen to its tissues, control bleeding, or fight infections. There are four common types of leukemia, which are grouped based on how quickly the disease gets worse (acute or chronic) and on the type of blood cell the cancer starts in (lymphoblastic or myeloid). Our page on leukemia has more information. Lymphoma Lymphoma is cancer that begins in lymphocytes (T cells or B cells). These are disease-fighting white blood cells that are part of the immune system. In lymphoma, abnormal lymphocytes build up in lymph nodes and lymph vessels, as well as in other organs of the body. There are two main types of lymphoma: Hodgkin lymphoma – People with this disease have abnormal lymphocytes that are called Reed-Sternberg cells. These cells usually form from B cells. Non-Hodgkin lymphoma – This is a large group of cancers that start in lymphocytes. The cancers can grow quickly or slowly and can form from B cells or T cells.

Our page on lymphoma has more information. Multiple Myeloma Multiple myeloma is cancer that begins in plasma cells , another type of immune cell. The abnormal plasma cells, called myeloma cells, build up in the bone marrow and form tumors in bones all through the body. Multiple myeloma is also called plasma cell myeloma and Kahler disease. Our page on multiple myeloma and other plasma cell neoplasms has more information. Melanoma Melanoma is cancer that begins in cells that become melanocytes, which are specialized cells that make melanin (the pigment that gives skin its color). Most melanomas form on the skin, but melanomas can also form in other pigmented tissues, such as the eye. Our pages on skin cancer and intraocular melanoma have more information. Brain and Spinal Cord Tumors There are different types of brain and spinal cord tumors. These tumors are named based on the type of cell in which they formed and where the tumor first formed in the central nervous system. For example, an astrocytic tumor begins in star-shaped brain cells called astrocytes , which help keep nerve cells healthy. Brain tumors can be benign (not cancer) or malignant (cancer).

Other Types of Tumors Germ Cell Tumors Germ cell tumors are a type of tumor that begins in the cells that give rise to sperm or eggs. These tumors can occur almost anywhere in the body and can be either benign or malignant. Our page of cancers by body location/system includes a list of germ cell tumors with links to more information. Neuroendocrine Tumors Neuroendocrine tumors form from cells that release hormones into the blood in response to a signal from the nervous system. These tumors, which may make higher-than-normal amounts of hormones, can cause many different symptoms. Neuroendocrine tumors may be benign or malignant. Our definition of neuroendocrine tumors has more information. Carcinoid Tumors Carcinoid tumors are a type of neuroendocrine tumor. They are slow-growing tumors that are usually found in the gastrointestinal system (most often in the rectum and small intestine). Carcinoid tumors may spread to the liver or other sites in the body, and they may secrete substances such as serotonin or prostaglandins, causing carcinoid syndrome .

Oncology - definition of oncology by The Free Dictionary Oncology - definition of oncology by The Free Dictionary (ŏn-kŏl′ə-jē, ŏng-) n. The branch of medicine that deals with tumors, including study of their development, diagnosis, treatment, and prevention. [Greek onkos, mass, tumor; see nek-3 in the Appendix of Indo-European roots + -logy .] on′co·log′i·cal (-kə-lŏj′ĭ-kəl), on′co·log′ic (-lŏj′ĭk) adj. on·col′o·gist n. oncology (Medicine) the branch of medicine concerned with the study, classification, and treatment of tumours oncological adj the branch of medical science dealing with tumors, including the diagnosis and treatment of cancer. [1855] on`co•log′ic (-kəˈlɒdʒ ɪk) on`co•log′i•cal, adj. on•col′o•gist, n. on·col·o·gy The branch of medicine that deals with the diagnosis and treatment of cancer. oncology 1.

the study of tumors. 2. the totality of medical knowledge concerning tumors. — oncologist, n. — oncologic, adj. Cancer: MedlinePlus Patient Handouts Summary Cancer begins in your cells, which are the building blocks of your body. Normally, your body forms new cells as you need them, replacing old cells that die. Sometimes this process goes wrong. New cells grow even when you don't need them, and old cells don't die when they should. These extra cells can form a mass called a tumor. Tumors can be benign or malignant. Benign tumors aren't cancer while malignant ones are. Cells from malignant tumors can invade nearby tissues. They can also break away and spread to other parts of the body. Cancer is not just one disease but many diseases. There are more than 100 different types of cancer. Most cancers are named for where they start. For example, lung cancer starts in the lung, and breast cancer starts in the breast. The spread of cancer from one part of the body to another is called metastasis. Symptoms and treatment depend on the cancer type and how advanced it is. Most treatment plans may include surgery, radiation and/or chemotherapy .

Some may involve hormone therapy, immunotherapy or other types of biologic therapy, or stem cell transplantation . NIH: National Cancer Institute Obesity and Cancer Risk - National Cancer Institute Obesity and Cancer Risk How is NCI studying and supporting research on obesity and cancer risk, and supporting research to understand the populations most at risk? What is obesity? Obesity is a condition in which a person has an abnormally high and unhealthy proportion of body fat. To measure obesity, researchers commonly use a scale known as the body mass index (BMI). BMI is calculated by dividing a person’s weight (in kilograms) by their height (in meters) squared. BMI provides a more accurate measure of obesity or being overweight than weight alone. Guidelines established by the National Institutes of Health (NIH) place adults age 20 and older into the following categories based on their BMI: BMI Obese The National Heart Lung and Blood Institute provides a BMI calculator .

For children and adolescents (less than 20 years of age), overweight and obesity are based on the Centers for Disease Control and Prevention’s (CDC) BMI-for-age growth charts : BMI BMI-for-age at or above sex-specific 85th percentile, but less than 95th percentile Overweight BMI-for-age at or above sex-specific 95th percentile Obese Compared with people of normal weight, those who are overweight or obese are at greater risk for many diseases, including diabetes, high blood pressure, cardiovascular diseases, stroke, and certain cancers. How common is overweight or obesity? Results from the 2007-2008 National Health and Nutrition Examination Survey (NHANES) show that 68 percent of U.S. adults age 20 years and older are overweight or obese. In 1988-1994, by contrast, only 56 percent of adults age 20 and older were overweight or obese. In addition, the percentage of children who are overweight or obese has also increased. Among children and teens ages 2 to 19, 17 percent are estimated to be obese, based on the 2007–2008 survey.

In 1988–1994, that figure was only 10 percent. What is known about the relationship between obesity and cancer? Obesity is associated with increased risks of the following cancer types, and possibly others as well: Esophagus Thyroid Gallbladder One study, using NCI Surveillance, Epidemiology, and End Results (SEER) data, estimated that in 2007 in the United States, about 34,000 new cases of cancer in men (4 percent) and 50,500 in women (7 percent) were due to obesity. The percentage of cases attributed to obesity varied widely for different cancer types but was as high as 40 percent for some cancers, particularly endometrial cancer and esophageal adenocarcinoma. A projection of the future health and economic burden of obesity in 2030 estimated that continuation of existing trends in obesity will lead to about 500,000 additional cases of cancer in the United States by 2030.

This analysis also found that if every adult reduced their BMI by 1 percent, which would be equivalent to a weight loss of roughly 1 kg (or 2.2 lbs) for an adult of average weight, this would prevent the increase in the number of cancer cases and actually result in the avoidance of about 100,000 new cases of cancer. Several possible mechanisms have been suggested to explain the association of obesity with increased risk of certain cancers: Fat tissue produces excess amounts of estrogen, high levels of which have been associated with the risk of breast, endometrial, and some other cancers. Obese people often have increased levels of insulin and insulin-like growth factor -1 (IGF-1) in their blood (a condition known as hyperinsulinemia or insulin resistance), which may promote the development of certain tumors. Fat cells produce hormones, called adipokines, that may stimulate or inhibit cell growth. For example, leptin, which is more abundant in obese people, seems to promote cell proliferation, whereas adiponectin, which is less abundant in obese people, may have antiproliferative effects.

Fat cells may also have direct and indirect effects on other tumor growth regulators, including mammalian target of rapamycin (mTOR) and AMP-activated protein kinase . Obese people often have chronic low-level, or “subacute,” inflammation, which has been associated with increased cancer risk. Other possible mechanisms include altered immune responses, effects on the nuclear factor kappa beta system, and oxidative stress . What is known about the relationship between obesity and breast cancer? Many studies have shown that overweight and obesity are associated with a modest increase in risk of postmenopausal breast cancer. This higher risk is seen mainly in women who have never used menopausal hormone therapy (MHT) and for tumors that express both estrogen and progesterone receptors. Overweight and obesity have, by contrast, been found to be associated with a reduced risk of premenopausal breast cancer in some studies. The relationship between obesity and breast cancer may be affected by the stage of life in which a woman gains weight and becomes obese. Epidemiologists are actively working to address this question. Weight gain during adult life, most often from about age 18 to between the ages of 50 and 60, has been consistently associated with risk of breast cancer after menopause.

The increased risk of postmenopausal breast cancer is thought to be due to increased levels of estrogen in obese women. After menopause, when the ovaries stop producing hormones, fat tissue becomes the most important source of estrogen. Because obese women have more fat tissue, their estrogen levels are higher, potentially leading to more rapid growth of estrogen-responsive breast tumors. The relationship between obesity and breast cancer risk may also vary by race and ethnicity. There is limited evidence that the risk associated with overweight and obesity may be less among African American and Hispanic women than among white women. What is known about the relationship between obesity and endometrial cancer? Overweight and obesity have been consistently associated with endometrial cancer, which is cancer of the lining of the uterus. Obese and overweight women have two to four times the risk of developing this disease than women of a normal weight, regardless of menopausal status. Many studies have also found that the risk of endometrial cancer increases with increasing weight gain in adulthood, particularly among women who have never used MHT. Although it has not yet been determined why obesity is a risk factor for endometrial cancer, some evidence points to a role for diabetes, possibly in combination with low levels of physical activity.

High levels of estrogen produced by fat tissue are also likely to play a role. What is known about the relationship between obesity and colorectal cancer? Among men, a higher BMI is strongly associated with increased risk of colorectal cancer. The distribution of body fat appears to be an important factor, with abdominal obesity, which can be measured by waist circumference, showing the strongest association with colon cancer risk. An association between BMI and waist circumference with colon cancer risk is also seen in women, but it is weaker. Use of MHT may modify the association in postmenopausal women. A number of mechanisms have been proposed to account for the association of obesity with increased colon cancer risk. One hypothesis is that high levels of insulin or insulin-related growth factors in obese people may promote colon cancer development. High BMI is also associated with rectal cancer risk, but the increase in risk is more modest. What is known about the relationship between obesity and kidney cancer? Obesity has been consistently associated with renal cell cancer, which is the most common form of kidney cancer, in both men and women. The mechanisms by which obesity may increase renal cell cancer risk are not well understood.

High blood pressure is a known risk factor for renal cell cancer, but the relationship between obesity and kidney cancer is independent of blood pressure status. High levels of insulin may play a role in the development of the disease. What is known about the relationship between obesity and esophageal cancer? Overweight and obese people are about twice as likely as people of healthy weight to develop a type of esophageal cancer called esophageal adenocarcinoma. Most studies have observed no increased risk, or even a decline in risk, with obesity for the other major type of esophageal cancer, squamous cell cancer. The mechanisms by which obesity may increase risk of esophageal adenocarcinoma are not well understood. However, overweight and obese people are more likely than people of normal weight to have a history of gastroesophageal reflux disease or Barrett esophagus , which are associated with an increased risk of esophageal adenocarcinoma. It is possible that obesity exacerbates the esophageal inflammation that is associated with these conditions. What is known about the relationship between obesity and pancreatic cancer? Many studies have reported a slight increase in risk of pancreatic cancer among overweight and obese individuals.

Waist circumference may be a particularly important factor in the association of overweight and obesity with pancreatic cancer. What is known about the relationship between obesity and thyroid cancer? Increasing weight has been found to be associated with an increase in the risk of thyroid cancer. It is unclear what the mechanism might be. What is known about the relationship between obesity and gallbladder cancer? The risk of gallbladder cancer increases with increasing BMI. The increase in risk may be due to the higher frequency of gallstones, a strong risk factor for gallbladder cancer, in obese individuals. What is known about the relationship between obesity and other cancers? The relationship between obesity and prostate cancer has been studied extensively. The results of individual studies do not suggest a consistent association between obesity and prostate cancer. However, when the data from multiple studies are pooled, analyses show that obesity may be associated with a very slight increase in the risk of prostate cancer. In addition, several studies have found that obese men have a higher risk of aggressive prostate cancer than men of healthy weight. Generally, risk of prostate cancer has been linked to levels of certain hormones and growth factors, especially IGF-1.

Some studies have shown a weak association between increasing BMI and risk of ovarian cancer, especially in premenopausal women, although other studies have not found an association. As with some other cancers, an association between ovarian cancer and obesity may reflect increased levels of estrogens. Some evidence links obesity to liver cancer and to some types of lymphoma and leukemia, but additional studies are needed to confirm these associations. Does avoiding weight gain or losing weight decrease the risk of cancer? The most conclusive way to test whether avoiding weight gain or losing weight will decrease the risk of cancer is through a controlled clinical trial . A number of NIH-funded weight loss trials have demonstrated that people can lose weight and that losing weight reduces their risk of developing chronic diseases, such as diabetes, while improving their risk factors for cardiovascular disease. However, previous trials and the results of an NCI workshop have demonstrated that it would not be feasible to conduct a weight loss trial of cancer prevention. The reason is that the effect of weight loss on the prevention of other chronic diseases would be demonstrated—and the trial consequently stopped so that the public could be informed of the benefits—before the effect on the prevention of cancer would become evident.

Therefore, most data about whether losing weight or avoiding weight gain prevents cancer come mainly from cohort and case-control studies. Data from these types of studies, called observational studies, can be difficult to interpret because people who lose weight or avoid weight gain may be different in other ways from people who do not, just as obese people may differ from lean people in other ways than BMI. That is, it is possible that these other differences explain their different cancer risk. Nevertheless, many observational studies have shown that people who have a lower weight gain during adulthood have a lower risk of: Colon cancer Breast cancer (after menopause) Endometrial cancer A more limited number of observational studies have examined the relationship between weight loss and cancer risk, and a few have found decreased risks of breast cancer and colon cancer among people who have lost weight. However, most of these studies have not been able to evaluate whether the weight loss was intentional or related to underlying health problems. Stronger evidence comes from studies of patients who have undergone bariatric surgery to lose weight. Obese people who have bariatric surgery appear to have lower rates of obesity-related cancers than obese people who did not have bariatric surgery.

It is important to note that whereas most lifestyle weight loss interventions result in weight losses of 7-10 percent of body weight, weight loss from bariatric surgery combined with lifestyle changes generally results in weight loss of 30 percent. How is NCI studying and supporting research on obesity and cancer risk, and supporting research to understand the populations most at risk? NCI supports research on obesity and cancer risk through a variety of activities, including large cooperative initiatives, web and data resources, extramural and intramural epidemiologic studies, basic science, and dissemination and implementation resources. The Institute has also issued a number of competitive funding opportunities related to obesity and cancer risk. In addition, NCI is an active participant in the NIH Obesity Research Task Force and played an active role in the development of the 2011 Strategic Plan for NIH Obesity Research . NCI-supported projects are outlined below. NCI-Funded Initiatives

Question: Oncology is the study of what?
Answer: Cancer